One reference is here: http://en.wikipedia.org/wiki/Energy_condition http://en.wikipedia.org/wiki/Energy_condition These conditions are widely believed to appl

One reference is here: http://en.wikipedia.org/wiki/Energy_condition http://en.wikipedia.org/wiki/Energy_condition These conditions are widely believed to apply to all realistic matter configurations (to the extent that the less-restrictive ones get used as postulates in some theorems in relativity), though there are some exceptions due to quantum effects (which I believe are usually short-lived). Just for example, a cosmological constant or other dark energy source does not violate the null energy condition. It would be really cool to see any of the energy conditions violated for an extended time in a lab! I'm pretty sure, though, that it has not yet been done.